In vitro susceptibility of methicillin-resistant Staphylococcus aureus to imipenem and other antimicrobial agents

Minimum inhibitory (MIC) and minimum bactericidal (MBC) concentrations of imipenem, pefloxacin, BMY 28142, were compared with those of vancomycin and other established antistaphylococcal antimicrobial agents, rifampicin, fusidic acid, clindamycin, tobramycin and amikacin against 50 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Imipenem was more active than the other tested antimicrobial agents except for vancomycin which was the most active. The MIC90 of imipenem was 2 micrograms/ml, while the MBC90 was 4.2 micrograms/ml and in all cases the MBCs were only 2-4 times higher than the MICs. Pefloxacin had significant bacteriostatic and bactericidal effect against the majority of the isolates, with an MIC90 of 12.5 micrograms/ml (range 0.4-25 micrograms/ml) and in most cases the bactericidal concentrations were 2-4 times the MIC, with a few isolates having MBCs 8 or more times the MICs. The results obtained confirm that imipenem has excellent in vitro activity against locally isolated MRSA.